Old thread and there is hardly any info out there but because this is the only link that comes up with a Google search, I figured I'd share my solution.
The solution is renaming pxelinux.com to pxeboot.com (effectively replacing it) in your \\Reminst\SMS Boot\ folder.
I used syslinux 6.03 with the syslinux components being from the bios subfolders (not EFI!).